Target for projectiles



March 5, 1957 L. G. SlMJlAN 2,734,000

TARGET FOR PROJECTILES Filed July 21," 1953 4 Sheets-Sheet 1 FIG. I

Amplifier Amplifier DIRECTION 33 DISTANCE PROJECTOR LUTHER C. SIMJIANINVENTOR BY-WM.

ATTORNEY March 5, 1957 L. 5. SIMJIAN 2,784,000

TARGET FOR PROJECTILES Filed July 21, 1953 4 Sheets-Sheet 2 LUTHER G.SIMJIAN INVENTOR ATTORNEY March 1957 L. G. SlMJlAN 2,784,000

TARGET FOR PROJECTILES Filed July 21, 1953 4 Sheets-Sheet 3 FIG.3

LUTHER G. SIMJIAN INVENTOR ATTORNEY Mam]! 19'57 1.. s. SIMJIAN 2,784,000

TARGET FOR PROJECTILES Filed July 21, 1953 4 Sheets-Sheet 4 FIG. 4 FIG.5

2 as as a? Ummcncnznzu:

FIG. 2 OUTPUT (Volts) FIG. 3

FREQUENCY LUTHER G. SIMJIAN INVENTOR BY M ATTORNEY TARGET FenPROJECTILES Luther G. Simjian, Greenwich, Conn., assignor to TheReflectone Corporation, Stamford, Comm, a corporation of ConnecticutApplication July 21, 1953, Serial No. 369,435 4 Claims. (Cl. 273-181)This invention relates to targets for projectiles and has particularreference to targets used in indoor games such as golf. The targets maybe used in conjunction with a computing system and a projection devicewhich indicates the free flight of the propelled object.

Several simple devices have been used to permit golf players to practiceindoors. These devices have not been accurate in predicting the velocityof the ball and they have not given a good indication of the ball inflight.

One of the objects of this invention is to provide an improved targetfor projectiles which avoids one or more of the disadvantages andlimitations of prior art games.

Another object of the invention is to increase the accuracy ofprojectile targets so that the projectile impact position may bedetermined within a narrow range of values.

Another object of the invention is to provide a target for projectileswhich can be used to determine the horizontal and vertical components ofthe impact position on the target so that other characteristics of theprojectile may be determined.

Another object of the invention is to determine the spin given to astruck golf ball.

Another object of the invention is to reduce the cost of projectiletargets by eliminating all electric contacts from the target impactareas.

Another object of the invention is to ruggedize projectile targets sothat they can withstand considerable shock and abuse without impairingthe quality of their response.

One feature of the invention comprises a series of three targets set atan angle to each other for determining horizontal direction, verticaldirection, and spin.

Another feature of the invention includes a target which is composed ofa plurality of tuned strips, each tuned to vibrate when struck at adifferent characteristic frequency. The strips are mounted adjacent tothe openings of a number of resonant chambers which filter the soundgiven off by the strips by suppressing those frequencies which differfrom the frequency to which the adjacent strip is tuned. A microphonepicks up the sound generated and transfers it to a computing system.

For a better understanding of the present invention together with otherand further objects thereof, reference is made to the followingdescription taken in connection with the accompanying drawings.

Fig. 1 is a schematic diagram showing some parts in section and thecircuits in block of the entire system.

Figs. 2 and 3 when taken together form a schematic diagram ofconnections of the computing system.

Fig. 4 is a side view in section showing an assembly of target stripsand the associated resonant chambers.

Fig. 5 is a schematic diagram of the projector used to show the flightof a golf ball on a screen.

Fig. 6 is a schematic diagram of connections showing a limiter and adiscriminator circuit which transforms a variable frequency into avariable amplitude wave.

Fig. 7 is a graph showing the relationship between the 2,784,000Patented Mar. 5, 1957 output voltage of the discriminator circuit andthe frequency of the input.

Fig. 8 is a diagram showing how Figs. 2 and 3 should be combined.

Referring now to Fig. 1 a ball 10 is supported on a tee 11 which issecured on a baseboard 12. In close proximity to the ball 10 amicrophone 13 is mounted which receives the noise generated by a clubstriking the ball and communicates this effect to an amplifier 14. Theamplifier is connected to a computing circuit 15 which determinesvelocity and distance and will be described in detail hereinafter.

The ball 10 is struck so that it moves in a general direction indicatedby an arrow 16 and first strikes a target 18. This target is composed ofa plurality of tuned strips 20 which are resiliently mounted in asubstantially longitudinal direction so that they may vibrate at acharacteristic frequency when struck by a ball. The strips are closelyspaced but do not touch one another.

Directly behind the array of strips a series of resonant chambers 21 ismounted. The details of the resonant chambers are shown in Fig. 4 wherethe strips 20 are mounted adjacent to the open ends of a plurality ofmetal tubes 21 each having a different length, and each arranged tovibrate with the same frequency as the tuned strips. The other ends ofthe resonant chambers are connected to a common chamber 22 in which ismounted a microphone 23. It will be obvious that when the ball strikes astrip 20 it will vibrate at a characteristic frequency and produce soundwaves which are filtered as described above by the resonant chamberadjacent to the struck strip. The microphone 23 then transmitselectrical vibrations of the same frequency to its amplifier,discriminator, and computer circuit.

After striking one of the strips in target 18 the ball bounces to asecond target 24 which is composed of a similar plurality of tunedstrips comprising target 24-. These strips are mounted in a transversedirection adjacent to a set of resonant chambers similar to set 21previously described but not 'visible'in Fig. l. The tuned stripscomprising target 24 are mounted horizontally in generally verticalalignment and are used to determine the vertical component of the ballstrajectory. The sound generated by target 24 is picked up by amicrophone 25 and amplified and transformed by the discriminator circuit26 (see Fig. 2).

After the ball 10 strikes target 24 it bounces to target 27 which iscomposed of strips similar to the strips 20 in target 18. The strips intarget 27 are arranged in a direction generally at right angles to thestrips in target 24 and are used to determine the spin given to the ball10 when it is struck. The strips in target 27 are backed by an array ofresonant chambers similar to chambers 21 and a microphone 28 (Fig. 2)picks up the sound waves and transfers electrical variations of the samefrequency to an amplifier circuit 30.

When the ball strikes target 18 a sound is genera-ted having acharacteristic frequency which determines the direction of the ball. Thesound frequency is transformed by microphone 23 and transmitted to anamplifier discriminator circuit 31 the output of which is connected totwo computer circuits, one circuit 32 for determining direction and asecond circuit 33 which determines spin. The output of amplifier 26 isused-to determine the vertical component of theballs trajectory andtherefore this information is connected to computer circuit 34 labeledloft. The output of amplifier 26 is also used to determine velocity anddistance by using the time interval between the time the ball is hit andthe time the ballstrlkes target 24, and for this reason the output ofamplifier 26 is also connected to computer circuit 15 which measures thetime interval and computes both the velocity and, distance that the ballwould take in free flightf The computer circuits deliver four outputvoltages, the durations of which determine the trajectory as shown on ascreen. In order to show the approximate path as viewcdfrom the startposition'that the ball would take out of doors the projector iscontrolled by four motors 39, 35, 36, and 37. The optical components ofthe projector are contained in a housing 38 and include the usualwellknown structures. The horizontal directional component of thetrajectory is controlled by motor 37 which turns a shaft 4-6 and rotatesthe projector base 41 by means of a screw 42. The base 41 is free toturn around a vertical bolt 43.

The vertical component of the trajectory is controlled by motor 39 whichturns a shaft 44 having a screw thread which meshes with a worm gear ontheoutside of a nut 45 which turns on bolt 43 and raises or lowers therear end of the projector 38, to cause the spot representing the ball tomove in a vertical direction on screen 46. In order to lend realism tothe picture on the screen a scene representing a golf course may bepainted on the screen or may be projected on the screen by anotherprojector. Such a picture would be similar to the view that a golferwould have if he stood at a teeing-off position and looked at the cup inthe distance. In order to further stimulate the flight of a golf ballthe spot which represents the ball must be diminshed in size as itleaves the tee. This action is controlled by motor 35 which is in turncontrolled by computer circuit 15. The motor 35, shown in greater detailin Fig. 5, operates a shaft 50 which turns a spiral gear meshing with aniris diaphragm 51.

Whena ball is driven from tee 11 and is given a spin to the right orleft, corresponding to a hook or slice, the amount of such spin is madeevident by the difference in sound frequencies generated by targets 18and 27. If the ball is hit correctly, without side spin, it will firststrike the middle strip 20 in target 18 then bounce to target 24 andthen to target 27 where it will strike a tuned strip having the samefrequency as the strip in target 18. The voltage magnitudes transmittedby amplifiers 31 and 30 will be equal and the output from computercircuit 33 will be zero and motor 36 will not turn. However, if a spinis given to the ball to the right or left its direction will be changedwhen striking target 18 and the strip in target 27 will have a differentfrequency than the strip first struck in target 18. This combinationproduces outputs of different voltage magnitudes from amplifiers 30 and31 and motor 36 will turn to the right or left giving a resultant pathsimilar to the direction taken by a golf ball.

The circuit shown in Fig. 6 is a combination limiter and discriminatorand is fully described in the Radio Engineers Handbook, 1943, by F. E.Terman, published by McGraw-Hill Book (30., New York, N. Y., page 586.The circuit includes a microphone transformer 50, a limiter tube 51, anda discriminator circuit 52 which includes two tuned circuits, capacitor53 and inductor 54 forming one of the tuned circuits and inductor 55 andcapacitor 56 forming the other tuned circuit. Two vacuum tube diodes 57and 58 rectify the alternating current and produce a pulsating directcurrent on conductors 60 which comprise the output circuit of thediscriminator component. On targets 18 and 27 the two tuned circuits 53,54 and 55, 56 are tuned to the frequency of the central strip so that ifthis strip is struck by the ball no voltage will be produced on theoutput conductors. Target 24 determines the vertical component of thetrajectory and there is no central position to indicate a divergence tothe right or left. Accordingly the tuned circuits are tuned to afrequency outside the range of the tuned strips.

Referring now to Figs. 2 and 3 the entire computing circuit is showntogether with the three targets, the tee, and four microphones. Target24, shown at the top of Fig. 2, transmits sound energy to microphone anddiscriminator circuit 26, the output voltage from this circuit charginga capacitor 62. The magnitude of this charge is impressed on the secondgrid of amplifier tube 63, grid number one being modulated by a 60 cyclesource 64. The anode of tube 63 is connected by conductor 65 to winding66 of a motor 39. Winding 66 together with a 60 cycle winding 67 causethe motor to turn in a direction which lowers the rear end of projectortable 38 and causes the spot on screen 46 to move up indicating the riseof the ball into the air during its first movement. As capacitor 62discharges the voltage transmitted over conductor 65 will diminish untilthere is soon insufiicient energy to cause the motor to turn over. Aboutthis time another modulated voltage is applied over conductor 68 toWinding 76 which in conjunction with winding 6'7 causes the motor toreverse its direction and move the spot down. The generation of themodulated voltage on conductor 68 will be described later.

When the ball 10 is struck the sound of the club striking the ballcauses a large voltage to be transmitted from microphone 13 throughtransformer 71 and rectifier '72 to charge a capacitor 73 and therebycondition an amplifier tube 74 to conduct and cause current to flowthrough an anode battery 75, tube 74, relay 76, back to ground therebyoperating relay 76 and closing all four of its contacts. The charge oncapacitor 73 retains tube '74 in its conductive condition for a shorttime interval and relay 76 remains in its operated condition until relay77 is operated. Relay 77 is operated by current from battery 75, throughcontacts 79, winding 77, and ground. When relay 77 is operated it isheld by a locking circuit which may be traced from the positive terminalof battery 75, through reset contacts 78, contacts 80, relay winding 77and ground. This circuit holds relay 77 in its operated condition untilcontacts 78 are broken by the manual operation of reset button R1.

The operation of relay 77 actuates the second and third series ofcontacts 81 and 82, transferring conduction to the left. When relay 77is in its non-operated condition a capacitor 83 is connected to battery84 and when the relay is operated the capacitor voltage is applied tothe control electrode of a triode 85 causing it to be conductive andoperate a third relay 86, closing contacts 87. It should be noted thatrelays 76, 77, and 86 are all operated in sequence in a very short timewhich depends only upon the inertia of the relay armaturcs and not onthe velocity of the struck ball. As soon as contacts 87 are closed aholding circuit for relay 76 is completed which may be traced frombattery 75, through reset contacts 78, through contacts 88 on relay 76,over conductor 90, through contacts 87 on relay 86, over conductor 91,through winding 76, and ground. This holding circuit can be broken byopening either set of contacts 78 or 87.

When the ball travels from the tee 11 it first strikes target 18, thentarget 24, and when the second target is struck it generates sound whichis picked up by microphone 25, transformed by discriminator 26, andcharges capacitor 62 to a voltage which maintains pentodes 63 and 93 ina conductive condition for a time interval which is proportional to thevertical component of the balls trajectory. The time interval whichelapses between the striking of the ball at the tee and the striking oftarget 24 is inversely proportional to the velocity of the ball and thedistance it should travel in free flight. However, since the bottom oftarget 24 is closer to the tee than the top, a correction must be addedto compensate for the variable distance traveled. -Amplifier pentodes 93and 94 are arranged to provide this correction which is applied asfollows:

Capacitor 62 is connected to the control electrode of pentode 93 as wellas to a similar electrode in pentode 63 and when an impact of the ballcharges capacitor 62 to a voltage which is proportional to the verticalcomponent of the balls trajectory, this same voltage is applied topentode 93. This voltage is modulated in the pentode by a kilocycle wave(from source 98) and the output is applied to a control electrode ofpentode 94. The input circuit of this tube includes a small resistor 95and a rectifier element 96. Pentode 94 has its anode connected to oneside of capacitor 83 and when its control electrode is made morepositive, pentode 94 acts as a variable resistor in parallel with thecapacitor to neutralize its charge and reduce the potential of thecontrol electrode of triode 85, causing it to be non-conductive andthereby permitting the C relay 86 to be normalized, opening contacts 87and also normalizing the A relay 76. If the ball hits the target matnear the top edge a large voltage is applied to pentode 93 and a smallvoltage is transmitted to pentode 94. This results in a mediated anodecurrent which takes a longer time to change the charge on capacitor 83to the value which will cause the anode cathode current through tube 85to be lowered sufficiently to cause the C relay 86 to open contacts 87.If the ball strikes the target 24 near the bottom edge the smallercharging voltage on capacitor 62 results in a larger modulating currenton conductor 97 and a comparatively shorter time for the operation of Crelay 86. If a different arrangement of targets is used so that theangle of target 24 is reversed, the same kind of compensation results ifthe coupling between pentodes 93 and 94 is reversed by the use of thewell known cathode follower coupling.

The actuation of the A relay 76 closes contacts 100 which connect a 10kilocycle wave from a source 98, through a blocking capacitor 101 and aresistor 102, to the control electrode of a pentode 103. A rectifier 104protects the tube from voltage surges and clips the positive halves ofthe 10 kilocycle waves to produce a voltage wave Which is similar to asquare topped pulse.v The output of tube 103 is applied to a capacitor105 connected between ground and the common switch points of contacts81. When the B relay 77 is unactuated', capacitor 105 is fully chargedto the potential of battery 84 since it is connected through relaycontacts 81. At this time pentode 103 is nonconducting and the charge oncapacitor 105 is not reduced by the pentode circuit. When the A and Brelays 76 and 77 are actuated, the control electrode of pentode 103 israised in potential making the tube conductive and the upper terminal ofcapacitor 105 is switched by contacts 81 to a voltage divider 106.Capacitor 105 is now discharged at a fast rate through pentode 103 andat a slow rate through voltage divider 106. This condition is maintainedfor the duration of the flight of the missile from the tee to the target24. When the ball strikes target 24 (corrected time) the A relay 76 isnormalized and pentode 103 is made non-conducting stopping the fastdischarge therethrough. However, the slow discharge through the voltagedivider continues until the capacitor 105 is discharged. During thedischarge period triode 107 and tetrode 108 are made conductive by thealtered potential supplied by the voltage divider. Triode 107 acts as aphase inverter and its output circuit is connected to a tetrode 108which sends its output (modulated by 60 cycle source 64) over conductor68 to winding 70 on the Y motor 39. The result produced by this circuitis the following sequence: As soon as the ball hits target 24 amodulated current is sent over conductor 65 to winding 66 to move theimage of the ball upward on the screen at a slowly diminishing rate. Atthe same time current is supplied by tetrode 108 over conductor 63 towinding 70 which tends to turn the motor in the opposite direction.Because of the phase inversion by triode 107 the current through winding70 starts at a small value and gradually increases to a maximum. Becauseof these two currents the image of the ball on the screen first risesthen fialls in an of a ball in free flight as seen from the driving tee.

The horizontal directional component is supplied by target 18 and the Xmotor 37. When the ball hits one of approximate path the strips intarget 18, a characteristicsound frequency is generated. This is pickedup by microphone 23, transformed by discriminator 31, and the resultantvoltage is applied to capacitor 110 or capacitor 111, depending upon theposition of the struck strip; whether it is to the right or left of apredetermined central position. The voltage on either one of capacitors110 and 111 causes conduction of one of the pentodes 112 or 113 and acurrent thereby flows through one of the anode conductors 114 or 115, toone of the two windings 116 or 117 on motor 37, and the motor turns tothe right or left an amount which is proportional to the current in thewindings. Motor 37 controls the horizontal position and path of theprojected spot which is the image of the ball in free flight.

The X motor 36 is carried on the table or base which holds the projectorand is designed to add to or subtract from the positioning action of theX motor 37. The movement of the X motor is controlled by targets 18 and27 and the difierence in the impact signals of the two targetsdetermines the amount of curve (hook or slice) given to the ball and thepath the ball will take. In order to determine this difference thetarget 27 is provided with a microphone 28 and a discriminator circuit30 and the output of the discriminator is applied to two capacitors 120and 121 which control the curents through pentodes 122 and 123 in asimilar manner as described above in connection with target 18.

The output currents from the anodes of tubes 122 and 123 are appliedover conductors 124 and 125 to transformer windings 126 and 127therebyinducing voltages in secondary windings 130 and 131. Thesesecondary windings are in series with secondary windings 132 and 135which are coupled to primary windings 134 and 133 which are connected toconductors 114 and 115 in the X motor circuit. The operation of thistnansformer circuit is arranged to subtract the direction component assensed by target 18 from the direction component as sensed by target 27and the difference is applied to either one (or both) of X motorwindings 136, 137. If the ball strikes both central strips in targets 18and 27 there will be no voltages generated and neither motor will turn.If the ball strikes an olf-center strip (right) in target 18 and thecorresponding strip in target 27 the currents through conductors 115 and125 will be equal and motor X will turn but motor X will not.

The Z motor 35 controls only the size of the spot on the, screen henceits motor winding 138 is connected to conductor 65 and the anode ofpentode 63.

After the stroke has been made current in windings 66, 70, 116, 117,136, 137, and 138 is reduced to zero. The motion of the ball on a screenis duly noted and recorded. It is then necessary to reset the apparatusto be ready for another play. This resetting action is accomplished bymanually depressing five reset keys R1, R2, R3, R4, and R5. Reset key R1opens contacts 78 and breaks the rocking circuit for the A and B relays76 and 77. Reset Keys R2, R3, R4, and R5 are all connected to operaterelays which return the motor armatures to their original or Zeroposition. Let it be assumed that motor 39, which moves the image up anddown on the screen, has been turned out of its zero position in aclockwise direction to show an upward movement. As soon as this actionstarts contacts 140 and 141 are both closed by the movement of cams 142and 143. The closing of these contacts causes no current to flow untilthe reset button is pressed. Because of the dual field in motor 39 theprojector is first moved to raise the spot on the screen and then tolower it. The circuits are adjusted to stop the motor before the zeroposition is reached so that the image of the missile is still on thescreen. At this position the contacts 140 and 141 are still closed.

When the reset key 144 is depressed a circuit is completed from ground,through contacts 145, through 7 winding 146, then through contacts 141,and the positive terminal of a source of electrical power. This actuatesthe relay, closing three contacts, one of which 147 is a holding contactand holds the relay in its actuated condition until contacts 141 areopened. A second set of contacts 148 connect the positive terminal,through contacts 141 and 140 to a second relay winding 150, actuating itand transferring two contact points 151 and 152 to a second set ofcontacts. Conductor 153 is connected to the 60 cycle source 64 (see Fig.2) and the action of relay 159 reverses the polarity of the 60 cyclesource, applying an alternating voltage to winding 67 which is 180degrees out of phase with the normal operating voltage.

The third set of contacts 154 closed by relay winding 146 connectsground to the control electrode of pentode 63 by way of conductor 155.This makes the pentode conducting and a 60 cycle modulated wave is sentover anode conductor 65 to winding 66 of the Y motor 39 which causes anupward motion of the proiector during normal operation but now causes areverse motion because the current in field winding 67 has beenreversed. The result of this motion turns motor 39 to its zero position.As soon as the zero position is reached the cam face on cam wheel 143opens contacts 141 and both relays are normalized and the motor rotationis stopped because contacts 154 are opened and pentode 63 is renderedconducting. Motor 39 will always be reset by a continued motion in thereversed direction in order to regain its normal position. Motor 35,which operates to close the iris 51, '11 also have its directionreversed when it is reset. Motors 36 and 37, which move the projector tothe'right or left, will be reversed in the same manner and by the samecircuits as described above. If motor 36 is turned in a counterclockwisedirection to move the spot on the screen to the right, contacts 160remain open and the reversing relay 161 is not operated. This retainsthe 60 cycle current in field winding 162 in its normal phase and whencurrent is sent over conductor 163 to the left hand tube 122, the motoris turned clockwise to return it to its normal position. Motors 36 and37 operate in a similar manner.

During the regular operation of the circuit, motors 36 and 37 may bemoved in either direction to show the path of the ball and for thisreason they must have resetting means which permit resetting in either aclockwise or counterclockwise direction, Motors 35 and 39 will move froma zero position to a final position which is equivalent to a motion inone direction only and therefore their resetting means could besimplified by the omission of contact cam 142 and contacts 146, with theupper contact point of contacts 148 connected to relay winding 153.However, for the sake of uniformity, all resetting circuits are made thesame.

The computing and recording systems disclosed in this specification aresimilar to systems disclosed in a pending application, Serial No.341,410, filed March 10, 1953 by L. G. Simjian and now abandoned. Thetargets disclosed herein differ considerably from the targets disclosedin the above mentioned application but the conical arrangement of targetsurfaces disclosed therein may be applied to the present invention.

While there have been described and illustrated specific examples of theinvention, it will be obvious that various changes and modifications maybe made therein without departing from the field of the invention whichshould be limited only by the scope of the appended claims.

I claim:

1. A target for determining the approximateimpact position of a movingmissible comprising; a plurality of spaced strips mounted parallel toeach other so as to present a barrier to the missible; said strips tunedto vibrate at characteristic frequencies; said frequencies differingfrom each other by a discernible amount; said strips arranged in apredetermined pattern whereby the production of a frequency denotes aposition of impact; a microphone positioned adjacent to said strips andadapted to produce a signal having a frequency corresponding to thefrequency of the struck strip; circuit means including a frequencydiscriminator connected to said 'microphone which produce a signal whoseamplitude-is proportional to the frequency received, and means forapplying said signal to a controlled instrumentality.

2. A target for determining the approximate impact position of a movingmissile in one dimension comprising; a plurality of spaced stripsmounted parallel to each other so as to present a barrier to themissile; said strips tuned to vibrate at characteristic frequencies;said frequencies differing from each other by a discernible amount; saidstrips arranged in a predetermined pattern whereby the production of afrequency denotes a position of impact; a sound resonant chamberassociated with each of said strips; a microphone positioned inproximity to said chambers and adapted to produce a signal having afrequency corresponding to the frequency of the struck strip; circuitmeans including a frequency discriminator connected to said microphonefor receiving said signal and to produce a signal whose amplitude isproportional to the frequency received, and means for applying saidsignal to a controlled instrumentality.

3. A target for determining the approximate impact position of a movingmissile having a predetermined di rection in two dimensions comprising;two sets of spaced strips; each set including a plurality of stripsmounted parallel to each other and tuned to vibrate at characteristicfrequencies; said two sets of strips mounted for sequential impact ofthe missile and respectively disposed in substantially longitudinal andtransverse directions relative to said missile direction; saidfrequencies differing from each other by a discernible amount; saidstrips in both sets arranged in predetermined patterns whereby theproduction of a frequency denotes a position of impact; said sets ofstrips determining the horizontal and vertical components of themissiles impact position; two microphones, each positioned in proximityto one of said sets to produce signals corresponding to the frequenciesof the struck strips; circuit means including a frequency discriminatorconnected to each microphone which produce a signal whose amplitude isproportional to the frequency received, and means for applying saidsignals to a controlled instrumentality.

4. A target as set forth in claim 3 wherein a third set of strips ismounted in proximity to said two sets of strips for sequential impact bythe missile, said third set of strips disposed in substantiallylongitudinal direction relative to said predetermined direction fordetermining a second horizontal impact position of the missile, saidthird set of strips including a microphone adapted to produce a signalhaving a frequency corresponding to the frequency of a struck strip insaid third set of strips.

References Cited in the file of this patent UNITED STATES PATENTS954,997 Rice Apr. 12, 1910 2,248,053 Bales July 8, 1941 2,331,237Schaefer Oct. 5, 1943 2,448,587 Green Sept. 7, 1948 2,557,550 Leaver etal. June 19, 1951 2,581,738 Williams Jan. 8, 1952 FOREIGN PATENTS202,756 Great Britain Aug. 30, 1923 432,156 Great Britain July 22, 1935

